The present invention relates to a valve assembly. In particular, but not exclusively, the present invention relates to a valve assembly for location in a borehole of a well.
When it is desired to carry out work on a partially or fully cased borehole of an oil or gas well there is a requirement for provision of an isolation barrier in the bore, which barrier may take the form of a valve, or a dense or xe2x80x9cweightedxe2x80x9d fluid. Also, when tubing is installed on a production well, and the well is xe2x80x9ccompletedxe2x80x9d, health and safety regulations require that a barrier, typically referred to a xe2x80x9csafetyxe2x80x9d valve, is installed as part of the completion.
In the course or drilling a well, the bore will pass through formations of different porosities and containing fluids at different pressures. Surveys will have been carried out with the aim of predicting the properties of the different formations, and the density of the column of drilling fluid or mud being circulated in the bore during the drilling operation is typically selected such that the fluid pressure in the bore is slightly higher than the formation fluid which is expected to be encountered. However, there is always a risk that a formation will be at a higher or lower pressure than anticipated, or that different formations intersected by a single bore will be at significantly different pressures. If the bore intersects an unexpectedly low pressure formation, there may be a significant loss of drilling mud into the formation, at great expense to the drilling operator, and if the formation is gas or oil-bearing such an influx of mud may result in significant damage to the production capabilities of the formation on the other hand, encountering an unexpectedly high pressure formation, creating a xe2x80x9ckickxe2x80x9d in the bore, may result in a sudden influx of formation fluid to the bore, with potentially disasterous consequences.
There are various established steps and operations which may be implemented to control such situations. In some cases, it may be possible to chemically treat or plug a porous or low pressure formation, or to circulate higher density drilling fluid to prevent or limit influx of fluids from a high pressure formation. However, these procedures tend to be time consuming and expensive, and in some cases the condition may be such, for example a sudden high pressure or high volume influx, that the well must be capped and abandoned. If time and conditions permit, it may be possible to isolate a problem formation by running casing into the bore. However, each string of casing that is run into a bore reduces the available bore diameter, and running casing earlier than predicted will restrict the available bore diameter, possibly to the extent that the well cannot be completed, and also limits the possiblities for running subsequent casing strings in the event of further problem formations being encountered.
In a completed well that has been producing for some time, it is not unusual for corrosion or erosion of well components to occur, such that the tubing must be retrieved to permit refurbishment and repair, or xe2x80x9cwork overxe2x80x9d of the well. Clearly, the flow of production fluid from the well must be halted during work over. Generally, it in preferred to do this by isolating the lower end of the bore, which intersects the producing formation, by installing a plug in the lower end of the tubing; the tubing above the plug may then be removed. However, erosion and the build up of scale and other deposits in the tubing may make it impossible to set a plug in the tubing. Accordingly, it may then be necessary to xe2x80x9ckillxe2x80x9d the well, by filling the bore with relatively dense fluid, the hydrostatic pressure produced by the column of fluid preventing the production fluid from flowing into the bore. However, killing a well often contaminates or damages the producing formation, and may even reduce the production capabilites of the formation to the extend that the well is no longer commercially viable.
It is amongst the objects of the present invention to obviate or mitigate at least one of the foregoing disadvantages.
According to a first aspect of the present invention there is provided a well operating method comprising:
providing a valve in a tubing string;
running the tubing string into a cased bore;
sealing the tubing string in the cased bore;
closing the valve to isolate the lower end of the bore;
uncoupling the tubing string from the valve;
retrieving the tubing string;
running a replacement tubing string into the bore;
coupling the replacement tubing string to the valve; and
opening the valve to permit fluid communication between the lower end of the bore and the tubing string.
The invention thus permits well work over and the like without the requirement to run a plug or kill the well. The references to a cased bore and intended to encompass a drilled bore which has been lined or partially lined with casing, liner or other form of bore wall support or sealing arrangement.
The valve may also be utilised to assist in the running of the tubing, in the setting of packers, in testing of the tubing, and to allow circulation of a fluid cushion. The valve may then be opened, until it becomes necessary to isolate the lower portion of the bore.
Preferably, the tubing string is a production tubing string.
Preferably, the valve is located towards the lower end of the tubing string.
Preferably, the tubing string is sealed in the cased bore by a packer, which is preferably located adjacent the valve. The packer may be located above or below the valve.
According to another aspect of the present invention there is provided a bore-drilling method comprising:
providing a valve in bore-lining casing;
advancing the bore by drilling using a drill string passing through the valve;
retrieving the drill string through the valve;
closing the valve to isolate the lower end of the bore; and
opening the valve to reestablish fluid communication with the lower end of the bore.
This aspect if the invention is useful in dealing with xe2x80x9ckicksxe2x80x9d or other problems encountered while drilling. In the event of a kick, the drill string may be pulled back to above the valve and the valve closed. Thus, the problem formation may be isolated relatively quickly. With the protection of the valve in place the well may be circulated to the required mud weight, the valve then opened and the well returned to a controlled situation.
Preferably, the method further comprises the step of monitoring the bore for conditions indicative the bore encountering a problem formation. Such monitoring may include pressure monitoring, mud gas analysis, or any known monitoring method.
According to a still further aspect of the present invention provides a valve assembly for location in a borehole of a well, the assembly comprising:
a hollow elongate member for location in the borehole;
a valve comprising a valve member and a fluid actuated valve control mechanism adapted to be selectively actuated to move the valve member between an open and a closed configuration, for selectively allowing fluid flow through the hollow member;
a first hydraulic control conduit in fluid communication with the valve control mechanism for permitting actuation of the control mechanism to move the valve member to the open configuration, by application of a first control fluid; and
a second hydraulic control conduit in fluid communication with the valve control mechanism to move the valve member to the closed configuration, by application of a second control fluid.
Preferably the valve assembly is adapted to form part of or to be mounted to a string of tubular members. The tubular members may be bore-lining casing or liner, production tubing, drill tubing or drill pipe, or the like.
One or both of the first and second control fluids may be a hydraulic fluid, Alternatively, the control fluids may be well fluids.
Preferably, the hollow elongate member is tubular.
Preferably, the valve is adapted to contain pressure from both above and below.
The valve member may comprise a plate, generally circular in plan and arcuate in profile. The plate may be disposed in an annular or part annular cavity in a wall of the hollow member when the valve is in the open configuration, and is preferably isolated in the cavity, to protect the plate from well fluids and debris. Alternatively, where the hollow member does not have to serve as a pressure barrier to one side of the closed valve member, the wall of the hollow member may define an aperture to receive the open valve member, increasing the available internal diameter. In the closed configuration, the plate may be disposed substantially perpendicularly to the wall of the hollow member.
Preferably, the valve control mechanism comprises a plurality of fluid actuated movable elements, and most preferably the elements are adapted to move in a predetermined sequence in response to exposure to a common fluid pressure. Conveniently, this is achieved by the elements defining different, staggered piston areas, such that the pressure forces experienced by the elements are different.
Preferably, the valve control mechanism comprises one or more elements each defining oppositely acting piston areas in communication with respective control conduits, a differential fluid pressure force in one direction tending to move the element in that direction. The pistons may be located in respective chambers and the flow of fluid from the chambers may be controlled to control piston movement; if the chamber contains an incompressible fluid, the piston will not prove unless fluid can flow from the chamber.
The valve may be actuated between the open and closed configurations by the selective application of control fluid through a selected one of the first and second control conduits, whilst simultaneously removing fluid via the other one of said first and second control conduits.
One or both of the first and second control conduits may be adapted to extend out of the borehole, with the fluid control and supply apparatus being located at surface. Alternatively, supply of fluid to the conduits may be controlled by downhole valves, which may form part of a control unit. The valves may provide selective communication with tubing fluid, or annulus fluid, or fluid supplied from surface. The valves may be controlled by any appropriate means, for example by signals communicated via control lines from surface or remotely from surface, such as by radio or audio signals, pressure pulses or pressure cycling, or in response to sensed downhole conditions, for example a sudden loss or increase in tubing pressure. The control unit may be located above or below a packer positioned between tubing and casing or liner.
Preferably, the valve assembly further comprises a bypass vent which is selectively openable to permit flow between the interior and exterior of the hollow member on opening and closing of the valve member to provide a fluid path around the valve member. Thus, as the valve member is opened or closed, fluid pressure or flow may bypass the valve member. The valve member and valve seat thus do not experience the wear and erosion that would otherwise occur when the valve member was only partially open and impair the ability of the valve member to create an effective seal.
According to a yet further aspect of the present invention provides a valve assembly for location in a borehole of a well, the assembly comprising:
a hollow elongate member for location in the borehole;
a valve comprising a valve member and a fluid actuated valve control mechanism adapted to be selectively actuated to move the valve member between an open and a closed configuration, for selectively allowing fluid flow through the hollow member, the valve control mechanism comprising a plurality of fluid actuated movable elements adapted to move in a predetermined sequence in response to exposure to a common fluid pressure.
This aspect of the invention provides for an additional degree of control of downhole valves, and may equally be applied to other downhole devices.
Conveniently, the sequential movement of the elements is achieved by the elements defining different piston areas, such that the pressure forces experienced by the elements are different.
According to a yet further aspect of the present invention provides a valve assembly for location in a is borehole of a well, the assembly comprising:
a hollow elongate member for location in the borehole;
a valve comprising a valve member and a fluid actuated valve control mechanism adapted to be selectively actuated to move the valve member between an open and a closed configuration;
a bypass vent being selectively openable to permit an alternative flow path around the valve member on closing of the valve member to provide a fluid path around the valve member.